Consistently getting "increase buffer size" error message.

I am using a 2012 MacBook Pro OSX 8.5 with a LaCie 3tb Thunderbolt External hard Drive. ProTools 10.9. I can't even play 1 track without the error " increase Buffer Size" message popping up. I am an experienced ProTools user and have done all the suggested optimizing and settings. Other problems I encounter are slow response on adjusting plugins ( really noticeable on EQ). This happens no matter what interface I use ( even the built in sound card) . Has anyone else experienced this? Took the Laptop to Mac and they say there are no issues with it. I only have the plugins installed that came with ProTools. Any ideas will be greatly appreciated. Thanks!